This invention relates to chromium-nickel stainless steel and, more particularly, to a martensitic chromium-nickel steel which, in its annealed condition, can readily be shaped into a wide variety of parts and which, when age hardened, displays an unusual combination of readily attained hardness, strength, notch strength and toughness.
The outstanding aged hardness and strength of the alloy disclosed in U.S. Pat. No. 3,408,178, granted to L. P. Myers and K. J. Goda, Jr. on Oct. 29, 1968 and assigned to the assignee of this application, largely account for the commercial acceptance that alloy has achieved. It is also believed that the titanium present in that alloy contributes, to a major extent, to the attainment of the alloy's outstanding properties, but, because residual elements such as carbon, nitrogen and sulfur should be kept very low (e.g. less than 0.01%) in such titanium strengthened alloys, the resultant relatively high cost of the alloys has detracted from its general usefulness. At the present time, there is a substantial need for an alloy which is not so expensive to make and use, but yet has a good combination of mechanical and chemical properties. For example, the textile industry requires an alloy for making such parts as spinnerets and pack parts characterized by relatively low cost but capable of being hardened to at least Rockwell C 44, and, in that condition, having an impact strength in the longitudinal direction of at least 15 ft-lb and at least 5 ft-lb in the transverse direction, a 0.2% yield strength of at least about 200,000 psi and an ultimate tensile strength of at least about 210,000 psi. The ratio of notch tensile strength to ultimate tensile strength (NTS/UTS) of the alloy should be at least equal to one. The alloy in its annealed and unhardened condition, should be soft enough so that it can be shaped to form the desired parts.